Polybutene is generally prepared by polymerizing olefin components having a carbon atom number of 4 (C4), which are produced during a hydrocarbon degrading process, using a Friedel-Craft type catalyst and has a number average molecular weight (Mn) of about 300 to 5,000. When 1,3-butadiene is extracted from the C4-hydrocarbon materials which are produced in petroleum refining process (cracking of heavy oil) or Naphtha Cracking Center (NCC), the remaining raw material includes paraffins such as iso-butane, normal-butane(n-butane) and olefins such as 1-butene, 2-butene, and iso-butene. Among these, the iso-butene amount is about 20 to 50 weight %. The iso-butene is mostly used for preparation of polybutene or methyl-t-butyl ether (MTBE) which is used as an octane number enhancer. Since iso-butene, among the olefin components of C4, has the highest reactivity, the produced polybutene is mostly composed of the iso-butene unit. Further, iso-butene is used in the fields of petrochemical and specialty chemicals. Specifically, iso-butene is used to prepare ETB (Ethylene Glycol mono-t-butyl Ether), DETB (Diethylene Glycol mono-t-butyl Ether) which is a raw material for manufacturing an electronic cleaning agent, DIB (Diiso-butene), and IIR (Isobutylene Isoprene Rubber).
However, due to the recent development of shale gas, C2 hydrocarbons (ethylene, etc.) or C3 hydrocarbons (propylene, etc.) which was obtained from naphtha pyrolysis process, are being supplied at a low price. Due to this, the pyrolysis step (process) of naphtha loses competitiveness, and the naphtha cracking business is shrinking and the supply of iso-butene is decreased. So the price of iso-butene is increasing. Therefore, there is a demand for developing a method for efficiently utilizing or increasing iso-butene.
Meanwhile, in a C4 fraction produced during the catalytic cracking of heavy oil in an oil-refining process and in a C4 raffinate generated in a naphtha pyrolysis process, about 20 to 35% of 1-butene is included. The 1-butene deteriorates the productivity of polybutene, which makes it difficult to produce polybutene of high quality (high vinylidene amount and low halogen amount). In the past, since polybutene was mainly used for preparing adhesive, glue or insulating oil, conventional polybutene (Con.PB), which is not highly reactive, was mainly used. However, recently, a polar group is introduced into the polybutene so that the polybutene can be used for preparing an anti-scuff agent of engine oil, a viscosity index improver or a detergent. Therefore, the demand for high reactive polybutene (NRPB) is increasing.
One of the well-known products having the polar group is poly isobutenyl succinic anhydride (PIBSA) which is prepared by reacting polybutene with maleic anhydride. Most of fuel detergents or lubricating oil additives are prepared by using the PIBSA. The highly reactive polybutene in which the double bond of polybutene is located at the end of polybutene reacts directly with maleic anhydride, resulting in a high yield of PIBSA. On the other hand, in the case of a conventional polybutene in which the double bond is located in the interior of the polybutene, and in particular, the number of the alkyl groups substituted to the double bond is large, the reactivity of the polybutene is low due to steric hindrance. After chlorinating the polybutene with chlorine gas, PIBSA is prepared by reacting the chlorinated polybutene with maleic anhydride.
One way to increase the reactivity of polybutene is to locate the double bond at the end of the molecule to form a vinylidene group. Polybutene having a vinylidene amount of more than 70 mol % (that is, the number of vinylidene groups with respect to the total number of double bonds is 70%) is referred to a highly reactive polybutene. Polybutene having a vinylidene amount of 40 to 70 mol % is referred to a mid-reactive polybutene (MVPB, Mid Vinylidene Polybutene). Polybutene having a vinylidene amount of less than 40 mol % is referred to a low reactive polybutene. For production of highly reactive polybutene, generally, boron trifluoride (BF3) is used as a catalyst, and alcohols, ethers and the like are used as co-catalysts. Further, in the case of conventional polybutene (mid-reactive and low reactive polybutene), an aluminum trichloride (AlCl3) catalyst is generally used, which does not induce the double bond formation at terminal positions of the polybutene.
In both of the conventional polybutene and the highly reactive polybutene, product quality, productivity per unit catalyst, and productivity per unit raw material may be deteriorated due to normal-butene in the raw materials. The higher the iso-butene amount in the raw material, the better the product quality, the productivity per unit raw material, and the productivity per unit catalyst. It is preferable to increase the iso-butene amount in the raw material so as to increase the amount of vinylidene in the produced polybutene. The highly reactive polybutene having a high vinylidene amount can produce a high-quality product such as a lubricating oil and a fuel detergent. It is also preferable to reduce the fluoride amount in the produced polybutene. The fluoride is generated from the catalyst, and the halogen component may induce a corrosion of the reactor for preparing the detergents and the lubricants. To increase the productivity per raw material, to increase productivity per catalyst, or to decrease the chlorine amount in the product, it is preferable to increase the iso-butene amount in the raw material.
For removing 1-butene which has the greatest influence on the quality of polybutene, U.S. Pat. No. 5,674,955 discloses a method for producing a polybutene by using a raw material containing at least 5% of 1-butene and by reducing the 1-butene amount in the initial raw material to 20% or less through pretreatment of the raw material under the condition of using a halogen compound catalyst and that thereby it is possible to manufacture polybutene containing a high vinylidene amount and a low halogen amount. Further, U.S. Pat. No. 6,207,115 discloses the selective hydrogenation of a diolefin (butadiene, etc.) using an olefin conversion unit (OCU) and isomerization of 1-butene to 2-butene at the same time. Among the initial raw materials, 1-butene and iso-butene are difficult to separate due to their similar boiling points, but raw materials after isomerization can be easily separated into iso-butene and 2-butene using the difference in boiling point. In the case of general OCU, 2-butene separated at the bottom of the distillation column is relatively high in boiling point, so it is used to prepare propylene by reacting with ethylene and iso-butene separated at the upper part of the distillation column because of relatively low boiling point is used for producing polybutene.
On the other hand, to prepare high purity iso-butene, iso-butene may be separated from C4 mixture. For example, t-butyl alcohol (TBA) dehydration method combining a hydration reaction and a dehydration reaction, methyl t-butyl ether (MTBE) cracking method in which methanol is added to iso-butene using an acid catalyst and then cracked to obtain iso-butene and dehydrogenation of isobutane and so on are well known, however, all of them are expensive, and the price of polybutene is increased.